This study will evaluate the efficacy and safety of GSK256066 in the treatment of subjects with mild bronchial asthma, using a number of clinical and biological markers of efficacy.

Inclusion criteria

• Documented history of bronchial asthma, first diagnosed at least 6 months prior to the screening visit and currently being treated only with intermittent short-acting beta -agonist therapy by inhalation.
• Pre-bronchodilator FEV1 >75% of predicted at screening.
• Non-smoker
• Demonstration of a positive reaction to at least one allergen from a battery of allergens (including house dust mite, grass pollen and cat hair on skin prick testing at screening, or within 12 months of study start.
• Have Asthmatic response
• Able and willing to give written informed consent to take part in the study.
• Available to complete all study measurements.

Exclusion criteria:

• History of cardiovascular disease
• Clinically significant abnormalities in safety laboratory analysis at screening including any subject who has greater than "trace urine protein levels" following urinalysis at screening.
• History of hayfever
• The subject has tested positive for hepatitis C antibody or hepatitis B surface antigen.
• The subject has tested positive for HIV antibodies.
• The subject has positive drugs of abuse test.
• Subjects weighing less than 50kg are to be excluded from participating in the study.
• The subject has participated in a study with a new molecular entity during the previous 3 months.
• History of being unable to tolerate or complete methacholine, and/or allergen challenge tests.
• There is a risk of non-compliance with study medication or study procedures.
• History of blood donation (450 mL) within 2 months of starting the clinical study.
• The subject regularly drinks more than 28 units of alcohol in a week if male, or 21 units per week if female. One unit of alcohol is defined as a medium (125 ml) glass of wine, half a pint (250 ml) of beer or one measure (24 ml) of spirits.